The present invention relates generally to cable television systems. More particularly, the present invention provides an improved transmission technique, including a method, for editing digital video signals that can be used in a cable television network. Merely by way of example, the present invention can also be applied to a variety of other applications such as data broadcasting, digital TV broadcasts, Internet, and ADSL network switching, and other related information transmission techniques.
Conventional television delivery systems have been designed to deliver analog video/audio signals from a signal source to viewer television sets at numerous user locations. Conventional analog cable television delivery systems typically operate with an analog cable converter box in the viewer home which uses a television to display commonly known cable television programs such as HBO(trademark), ShowTime(trademark), and others. The converter box is connected via cable to an analog cable head end site, which often services a selected geographic region. Each analog cable head end site often has multiple satellite dishes, which normally receive transponded signals from one or more satellites. A satellite may have multiple satellite transponders that provide a group of viewer channels or programs to the head end. Although up link sites and satellite dishes can transmit and receive multiple video/audio program signals, some conventional satellite transponders generally carry only a single video/audio program at any given time. There is also generally one Integrated Receiver and Decoder per transponder (or channel) at the analog cable head end to receive the signal from the transponder.
Accordingly, conventional analog technology often requires a combination of one uplink site, one satellite transponder, and one cable head end satellite dish to deliver each analog video/audio program to the cable head end. The cable head end uses several analog video/audio signals from multiple dishes and multiple transponders to provide multi-channel analog signals. The cable head end then transmits these analog signals on different transmission frequencies to the cable converter boxes in the viewer homes where one channel is selected by the viewer. Accordingly, the viewer can selected programs such as those noted above (e.g., HBO(trademark)), but can also be others. Each television channel for analog video/audio transmissions for television is in a 6 MHz segment of bandwidth. An industry standard of 6 MHz was set in the late 1930""s and the NTSC standard is still 6 MHz per channel of analog video. As television program delivery technology moves from analog into the digital world, the conventional 6 MHz segments have no real technical significance, except in hybrid analog-digital converters.
In some selected geographic regions, digital video/audio systems to distribute digital video/audio have been used or proposed. Many of these system are based, in part, upon a standard made by the International Organization For Standardization (xe2x80x9cISOxe2x80x9d). This standard is commonly called the MPEG-2 protocol for combining one or more xe2x80x9celementary streamsxe2x80x9d of coded video, audio, or other data into a single bitstream suitable for transmission. The MPEG-2 standard provides a common syntax and set of semantic rules for the construction of bitstreams containing a multiplexed combination of one or more xe2x80x9cprograms,xe2x80x9d where the program is often composed of one or more related elementary streams, e.g., video, audio. Accordingly, it is possible to distribute digital video/audio signals to users using conventional digital video systems.
These conventional digital video systems, however, still have numerous limitations. As merely an example, conventional digital video systems do not generally have any effective editing capabilities. That is, digital video/audio signals derived from a cable television provider cannot easily be edited at, for example, a head end location. Additionally, some digital video systems do not have any local network information such as local stations and the like. Although these digital video systems may be useful in providing a user with a clear digital video signal for xe2x80x9ccablexe2x80x9d programs such as HBO(trademark) or ShowTime(trademark), they simply cannot and do not provide channels for location contents through the digital video system. Furthermore, most conventional digital video systems cannot provide xe2x80x9creal timexe2x80x9d editing capabilities without substantially interfering with the quality of the resulting video image. Some of these conventional cable systems also have constant bit rate information streams that are composed of variable bit rate stream that are often difficult or even impossible to edit using conventional technology. These and other limitations are described throughout the present specification, and more particularly below.
From the above, it can be seen that a cost effective, device for manipulating cable television signals is often desirable.
The present invention provides techniques for improved digital video transmission. More particularly, the present invention provides a method for editing video/audio information for a cable television system.
In a specific embodiment, the present invention provides a method for editing a first digital signal such as a constant bit rate digital signal in a cable head end. The present method uses a step of providing a first constant bit rate information stream (e.g., multiple constant bit rate streams), where the first constant bit rate stream includes a plurality of variable bit rate streams. Each of the variable bit rate streams corresponds to a program, e.g., television program. The method removes one or more of the variable bit rate streams from the first constant bit rate stream, and converts the first constant bit rate stream, without the one or more variable bit rate streams, into a second constant bit rate stream. A step of transferring the second constant bit rate stream to a user location is included. The present invention uses a transcoding technique to edit the first constant bit rate stream without interfering with video picture quality at the user location.
According to an embodiment of the present invention, the present method uses a technique for transcoding an input elementary stream such as the first constant bit rate stream. The method includes a variety of steps such as providing the input elementary stream such as the one noted, but can be others. A step of separating an input elementary stream into transform coefficients and their associated motion vectors is included. The method then includes steps of dequantizing the transform coefficients to form block transform coefficients, and determining a compensation stream using a feedback path. The method combines the compensation stream from the feedback path with the block transform coefficients to form a corrected stream. The correlated stream is reduced to form an output stream having a characteristic data rate different from the characteristic data rate of the input stream. The combination of these steps can provide a resultant digital video signal from the input stream.
In an alternative aspect, the present invention uses an editing method for transcoding one or more elementary streams, such as the first constant bit rate stream, having a characteristic input data rate in order to form an output elementary stream having an output data rate. The method includes a variety of steps such as separating the input elementary stream into motion vectors and transformation coefficients. An inverse quantization is performed on the transform coefficients to form block transform coefficients. A corrected stream is formed by summing the block transform coefficients with a compensation stream formed in a feedback loop. The corrected stream is reduced to form an output stream having a characteristic data rate equal to the target output data rate. An error representation is generated from dequantizing the output stream to form a second set of block transform coefficients, and then combining the block transform coefficients with the second set of block transform coefficients to form the error representation. The error representation is converted to a time domain representation. An error accumulation of successive frames is selectively computed by selecting a subset in both frames using the motion vectors and computing the error between these subsets. The error accumulation is converted to the compensation stream for feedback. Finally, the output stream and the motion vectors are combined to form the output elementary stream.
In a further embodiment, the present invention provides a method for editing a first constant bit rate signal using transcoding an input digital signal, such as the first constant bit rate stream, having an input data rate to form an output digital signal having an output data rate. The method includes a variety of steps such as separating the input digital signal to obtain a first transformed signal and a plurality of motion information. A step of correcting the first transformed signal with a compensation signal to generate a corrected signal is also included. The method then includes the steps of reducing the corrected signal to generate a second transformed signal and then generating an error signal based on the first transformed signal and the second transform signal, where the compensation signal is generated based upon the error signal and the motion information. The method then combines the second transformed digital signal and the motion information to form the output digital signal.
Still further, the present invention provides an editing method using transcoding an input digital signal (e.g., first constant bit rate stream) having an input data rate to form an output digital signal (e.g., second constant bit rate stream) having an output data rate. The method includes a variety of steps such as separating the input digital signal into a first transformed signal and a plurality of motion information. The method also includes the step of reducing the first transformed signal to form a second transformed signal having the output data rate. The method also includes the step of generating the output digital signal from the second transformed signal and the plurality of motion information.
Numerous benefits are achieved by way of the present invention over conventional techniques. In some embodiments, the present invention provides a method that is cost effective and can be implemented using relatively conventional hardware and software components. In other embodiments, the present invention can provide a resulting digital video/audio output that has been edited to provide the user a group of program channels that are desirable to the user. Furthermore, the present invention provides a transcoding technique to edit and insert local contents into the stream of information to be output to a user location in yet further embodiments. Depending upon the embodiment, the above benefits, as well as others, can be present in one or more embodiments. Each embodiment can also have one or more of the noted benefits, as well as others. These and other benefits are described throughout the present specification and more particularly below.
The invention will be better understood upon reference to the following detailed description and its accompanying drawings.